Combined Proton and Photon Radiotherapy for Orbital Granular Cell Tumor: A Case Report and Review of the Literature

Background Granular cell tumors (GCTs) are rare Schwann cell–derived neoplasms, with malignant variants comprising approximately 1–2% of cases. Orbital involvement is exceedingly uncommon, and optimal management remains undefined due to limited published experience. While maximal safe surgical resection is the primary treatment, complete excision may be precluded by proximity to critical structures such as the optic nerve and extraocular muscles. The role of adjuvant radiotherapy in malignant orbital GCT is not well established. Case Presentation: A 47-year-old man presented with progressive left orbital swelling, redness, and intermittent diplopia. Magnetic resonance imaging demonstrated a 3.1 × 2.4 × 2.0 cm heterogeneously enhancing left orbital mass. Orbitotomy with biopsy confirmed malignant GCT. Despite initial stability on imaging, interval progression with extraocular muscle invasion prompted subtotal surgical debulking with preservation of the optic nerve and globe. Given residual disease in close proximity to critical visual structures, the patient underwent a second combined endonasal and transorbital resection followed by adjuvant radiotherapy. He received proton beam therapy to 45 Gy in 25 fractions, followed by a sequential CyberKnife boost of 9 Gy in 5 fractions. Treatment was well tolerated. Serial imaging demonstrated sustained tumor regression, decreasing to 1.8 × 1.2 × 2.2 cm at seven months post-radiotherapy. At 22 months following initial orbitotomy and nearly one year after completion of radiotherapy, the lesion remained radiographically stable with continued response. Visual function was preserved, and no significant long-term radiation-related toxicity was observed. Conclusions Malignant orbital GCT is rare and poses significant surgical challenges when complete excision risks vision loss. This case demonstrates durable local control with subtotal resection followed by adjuvant proton therapy and stereotactic radiosurgical boost, with preservation of visual function. Multimodal therapy incorporating advanced radiation techniques may represent a viable strategy in select patients with anatomically constrained malignant orbital GCT. Further investigation is needed to better define the role and optimal dosing of radiotherapy in this setting.